Perennial ryegrasses (Lolium species), also called English ryegrass, is a temperate (cool-season) perennial grass that is native to Europe, temperate Asia, and North Africa. It has been widely distributed to other parts of the world, including North and South America, Europe, New Zealand, and Australia. Perennial ryegrass is valued for high yield potential, fast establishment, reduced tillage renovation applications, and use on heavy and waterlogged soils.
Two types of perennial ryegrasses, forage and turf, are most commonly grown. Forage-type perennial ryegrasses are important grasses in forage-livestock systems. High palatability and digestibility make this species highly valued for use in dairy and sheep forage systems. As a result, it often is the preferred forage grass in temperate regions of the world.
Use of perennial ryegrass for turf has increased in recent years with selection of more dense and persistent turf types. It is one of the most versatile of all turfgrass species. For turf, perennial ryegrass is used alone or in combination with other grasses. For the southern region of the U.S., perennial ryegrass's intolerance to high temperature has become an advantage; it is used to overseed dormant Bermuda grass (Cynodon dactylon) on Southern lawns and sports fields during the winter months. The perennial ryegrass thins and often dies during hot spring and summer weather, allowing the transition to Bermuda grass turf thus maintaining an active surface suitable for golf and other sports.
Glyphosate (N-(phosphonomethyl) glycine) is the active ingredient in glyphosate herbicides, such as ROUNDUP® brand herbicide produced by Monsanto (St. Louis, Mo.). Typically, glyphosate is formulated as a water-soluble salt such as an ammonium, alkylamine, alkali metal or trimethylsulfonium salt. One of the most common formulations is the isopropylamine salt of glyphosate, which is the form employed in ROUNDUP® brand herbicide.
Glyphosate is a broad spectrum herbicide that inhibits the enzyme enolpyruvylshikimate-phosphate synthase (ESPS). It is conventionally applied as an aqueous solution to the foliage of plants, where it is taken up into the leaves and transported throughout the plant. Commercial formulations of glyphosate may also include one or more surfactants to facilitate penetration of the active ingredient into the plant leaves, as well as compounds to enhance rainfastness. Numerous U.S. patents disclose various formulations of glyphosate, including U.S. Pat. Nos. 4,405,531; 5,118,338; 5,196,044; 5,639,711; 5,652,197; 5,679,621; and 5,750,468.
Little success has been reported in finding natural resistance to glyphosate herbicides in plants. This is beneficial in one respect since it indicates that the likelihood of glyphosate resistant populations of weeds arising is low, but it also means that few naturally resistant desirable plant species are available. As a result, great care must be taken when applying glyphosate herbicides in the vicinity of desirable plants (such as crops, ornamentals, and grass turf). Glyphosate herbicides are highly effective against all grass species and therefore have not been previously known to be applied to control weed growth in turf-type perennial ryegrasses.